Polyynes and cyanopolyynes synthesis from the submerged electric arc: about the role played by the electrodes and solvents in polyynes formation

The products of the electric arc between graphite electrodes have been investigated by high performance liquid chromatography-diode-array detector (HPLC-DAD) analysis in various media: distilled water, liquid nitrogen, methanol, ethanol, n-hexane and benzene. In distilled water, hydrogen capped polyynes H-(CC)_n-H were the unique products demonstrating that carbon is supplied by the graphite electrodes while hydrogen is supplied by the solvent plasmalysis (in this case water plasmalysis). Arcing graphite electrodes in liquid nitrogen produces cyanopolyynes: NC-(CC)_n-CN demonstrating that in this case the end groups of the polyyne chains are supplied by molecular nitrogen plasmalysis caused by the electric arc. Graphite arcing in methanol and ethanol produces very clean solutions (by-products negligible or absent) of hydrogen-capped polyynes with C₈H₂ as the main product accounting for more than 70 mol percent of the total polyyne concentration. By replacing graphite electrodes with titanium electrodes in methanol or in ethanol, polyynes are not formed at all; only trace amounts of polycyclic aromatic hydrocarbons (PAHs) were detected. When arcing with graphite electrodes is conducted in n-hexane or in benzene, polyyne formation is accompanied by a significant production of PAH, especially in benzene. These results have been rationalized in terms of carbonization or coking tendency of a given solvent. The effect of using titanium electrodes in place of graphite electrodes has been investigated also in n-hexane and in benzene as well as the effects of very high electric current intensity employed to ignite and sustain the submerged electric arc.     

Importance of electron correlation effects and basis set superposition error in calculations of interaction energies and interaction-induced electric properties in hydrogen-bonded complexes: a model study

A detailed study of the interaction energies and interaction-induced electric dipole properties in model linear hydrogen cyanide complexes (HCN) _m (m?=?2?C4) is carried out within the finite field HF SCF, MP2, CCSD and CCSD(T) approximations using the recently developed LPol-n (n?=?ds, fs, dl, fl) basis sets. The importance of high-order correlation effects and the basis set superposition error is evaluated. To correct for the latter is crucial for obtaining accurate interaction energy values, but the error can safely be neglected in the estimation of induced electric properties when the LPol-n (n?=?ds, fs, dl, fl) basis sets are used. Correlation effects are important in the evaluation of both the interaction energies and the induced electric properties of the systems.     

Alkane oxidation by the H2O2-NaVO3-H2SO4 system in acetonitrile and water

A simple system is described, which oxidizes saturated hydrocarbons either in acetonitrile or (less efficiently) in water. The system consists of 50% aqueous hydrogen peroxide as an oxidant, sodium metavanadate, NaVO₃, as a catalyst and sulfuric (or oxalic) acid as a co-catalyst. The reactions were carried out at 20-50 °C. In the oxidation of cyclohexane in acetonitrile, the highest yield (37% based on cyclohexane) and turnover number (TON=1700) were attained after 3 h at 50 °C. The corresponding parameters were 16% and 1090 for n-heptane oxidation under the same conditions. The oxidation of higher alkanes, RH, in acetonitrile gives almost exclusively the corresponding alkyl hydroperoxides, ROOH. Light alkanes (n-butane, propane, ethane, and methane) have been also oxygenated by the system under consideration. The highest TON (200) was attained for ethane and the highest yield (19%) was obtained in the case of n-butane. The selectivity parameters measured for the oxidation of linear and branched alkanes are low, the reaction with cis- and trans-1,2-dimethylcyclohexanes is not stereoselective. These facts lead us to conclude that the oxidation occurs with the formation of hydroxyl radicals in the crucial step.     

Cole-Cole plot analysis of dielectric behavior of monoalkyl ethers of polyethylene glycol (CnEm)

The complex permittivity of monoalkyl ether of polyethylene glycol (C_nE_m) was measured at 336.5 K at frequencies from 0.2 to 20 GHz. The number of bonded ethylene glycol units was varied from 1 to 120 to observe the effect of the PEG-chain length on the dielectric permittivity of the whole polymer. The measured real and imaginary parts of complex permittivity of these polymers were studied by the graphical analysis of the Cole-Cole plot as proposed by Havriliak and Negami. This analysis makes us understand that, in the high-frequency region above 9.7 GHz, the Cole-Cole plot of all C_nE_m is located on one single line. This phenomenon implies the same relaxation mechanism of all C_nE_m in this frequency region. It is found that the same relaxation mechanism of the dipoles of the hydroxyl group in n-alcohol contributes to the dipole relaxation of C_nE_m. In the low-frequency region, the arc of the Cole-Cole plot has the same shape as pure PEG, but it is scaled-down linearly following the decrease of the number of PEG units bonded to the n-alkanes. This phenomenon explains the linear contribution of ether dipoles, existing in bonded PEGs, on the complex permittivity of C_nE_m in the low-frequency region.     

The applicability of the “straight-line method” of asmus in the determination of the composition of polynuclear complexes

The straight-line method of Asmus was originally developed for the determination of n in mononuclear complexes of the general form AB_n (n≧ 1). In the present investigation it is demonstrated that the method also can be used for determining the value of n in polynuclear complexes of the form A[_mB_n (m > 1). The method as suggested by Asmus, is, however, not capable of distinguishing between mono- and polynuclear species. It is further shown, that the straight-line method can be applied for the determination of the value of m.     

Mobile phase selection for the combined use of liquid chromatography–inductively coupled plasma mass spectrometry and electrospray ionisation mass spectrometry

Four different organic solvents: dimethylformamide, 1,4-dioxane, n-propanol and ethanol were evaluated as alternative organic modifiers to acetonitrile for liquid chromatography (LC) separations. The aim was to establish common sets of chromatographic conditions that could be applied for LC hyphenation to inductively coupled plasma mass spectrometry (ICPMS) as well as to electrospray ionization MS (ESIMS). The approach was to evaluate candidate solvents that, compared to acetonitrile, potentially could give improved analytical performance (low solvent vapor loading, maximized analyte sensitivity and minimized carbon depositions on instrumental parts) in ICPMS analysis while retaining chromatographic and ESIMS performances. The study showed that dimethylformamide, 1,4-dioxane, n-propanol and ethanol all can be advantageous chromatographic modifiers for LC–ICPMS analysis, giving superior performance compared to acetonitrile. For the combined use of LC–ICPMS and LC–ESIMS with a common set of chromatographic conditions, n-propanol gave the best overall performance. The ¹⁹⁵Pt⁺ signal in ICPMS was continuously monitored during a 0–60% organic solvent gradient and at 25% of organic modifier, 100% of the signal obtained at the gradient start was preserved for n-propanol compared to only 35% of the signal when using acetonitrile. Platinum detection limits were 5–8 times lower using n-propanol compared with acetonitrile. Signal-to-noise ratio in continuous ESIMS signal measurements was 100, 90 and 110 for a 100 μg/ml solution of leucine–enkephaline using acetonitrile, ethanol and n-propanol, respectively. Chromatographic efficiency in reversed phase separations was preserved for n-propanol compared to acetonitrile for the analysis of the whole protein cytochrome C and the peptide bacitracin on a column with particle and pore sizes of 5 μm and 300 Å, but slightly deteriorated for the separation of the peptides leucine–enkephaline and bacitracin on a 3 μm and 90 Å column as the peak width at half height for both peptides increased by a factor of two. The performance on the smaller dimensioned column could however be improved by running the separations at 40 °C.     

Optical properties of green-blue-emitting Ca-α-Sialon:Ce,Li phosphors for white light-emitting diodes (LEDs)

Ce³⁺,Li⁺-codoped Ca-α-Sialon phosphors with the formula [Ca_(1−2x)Ce_xLi_x]_m/2Si_12−(m+n)Al_m+nO_nN_16−n (0≤x≤0.25, 0.5≤m≤3.5, and 0.16≤n≤2.0) have been synthesized by gas pressure sintering (GPS). The effects of the activator concentration and the overall composition of host lattice on the phase evolution, morphology, and optical properties were investigated. The single-phase Ca-α-Sialon:Ce³⁺,Li⁺ can be synthesized at x<0.1, 1.0≤m≤2.5, and n≤1.2. The synthesized powders exhibit a relatively dispersive and uniform morphology. Under the near UV excitation, the bright green-blue emission centered at 500-518 nm is observed. The photoluminescence can be tailored by controlling Ce³⁺ concentration and the overall composition of the α-Sialon host lattice. With increasing the Ce concentration and m value both excitation and emission bands show a red shift, which perfectly matches with the near-UV LEDs in the range of 360-410 nm. The strongest luminescence is achieved at x=0.08-0.1, m=2.0-2.5, and n=1.0. Simultaneously, the highest quantum efficiency and better thermal stability are also present.     

Excess Molar Volumes of Oligo(Oxyethylene Glycol) Monodecyl Ethers in n-Dodecane, and Apparent Dipole Moments of {(Oligo(Oxyethylene Glycol) Monodecyl Ethers?+?n-Heptane, n-Decane or n-Dodecane} at T?=?298.15?K

Excess molar volumes and relative permittivities at a frequency of 30?kHz of oligo(oxyethylene glycol) monodecyl ethers (C₁₀E _m ) for m?=?1?C8 in n-heptane, n-decane or n-dodecane solutions were determined for the mole fraction range 0?<?x?<?0.04 at the temperature of 298.15?K. By using Frohlich??s equation the apparent dipole moments, ??, of C₁₀E _m were calculated, and the limiting values, ?? ₀, were determined by extrapolating to infinite dilution. The values of ?? ₀ increase linearly with increasing number of oxyethylene units (m) of oligo(oxyethylene glycol) monodecyl ethers in the range m?=?2?C8, while ?? ₀ of C₁₀E₁ is less than its extrapolated value. By comparing the present results with our previous ones measured in n-heptane and decane, a solvent effect on ?? ₀ was found. The excess partial molar volumes of oligo(oxyethylene glycol) monodecyl ethers at infinite dilution increase with increasing m. Those results are discussed from the viewpoint of the interactions between oligo(oxyethylene glycol) monodecyl ethers and solvent molecules.     

Synthesis and characterization of partially fluorinated ethers

A series of partially fluorinated ethers PFE-m,n with general formula F(CF₂)_mCH₂CH₂O(CH₂)_nH (m = 4, 6, 8 and n = 2, 3, 5, 8, 14, 18, 21) has been synthesized and characterized. The present work aimed to investigate the synthesis of PFE-m,n and evaluate some of their fundamental physico-chemical properties such as: specific gravity, refractive index, viscosity, solid-solid transitions, solubility and amphiphile surface activity in a variety of solvents. Further, a comparison between PFE-m,n and the well known semifluorinated n-alkanes F(CF₂)_m-(CH₂)nH (FHm, n) with the same value of the m/n ratio have been reported.     

Synthesis and properties of gemini-type hydrocarbon-fluorocarbon hybrid surfactants

Gemini-type hybrid surfactants with two fluorocarbon chains connected through a hydrocarbon spacer, F(CF₂)_m(CH₂)₂CH(OSO₃Na)(CH₂)_nCH(OSO₃Na)(CH₂)₂(CF₂)_mF [Fm(Hn)FmOS, m = 4, 6; n = 5, 6, 7, 8)], were synthesized and their surface chemical properties were examined with the aim to have highly functional and highly water-soluble fluorinated surfactants when compared with the conventional fluorinated surfactants. Comparisons of the surface chemical properties of the synthesized gemini-type hybrid surfactants with those of monounit-type hybrid surfactants, F(CF₂)_m(CH₂)₂CH(OSO₃Na)(CH₂)_nH [FmEHnOS, m = 4, 6; n = 3, 5)], revealed that gemination causes a remarkable lowering (about 1/100) in cmc value while it produces little changes in Krafft point (below 0 °C) and surface tension at cmc (γ_cmc).     

Peroxidase activity-structure relationship of the intermolecular four-stranded G-quadruplex-hemin complexes and their application in Hg ion detection

The peroxidase activities of the complexes of hemin and intermolecular four-stranded G-quadruplexes formed by short-stranded X_nG_mX_p sequences (X = A, T or C), especially T_nG_mT_p sequences, were compared. The results, combining with those of circular dichroism (CD) spectra and acid-base transition study for DNA-hemin complexes, provide some important information about DNAzymes based on G-quadruplex-hemin complexes, such as the formation of a G-quadruplex structure is an important factor for determining whether a DNA sequence can enhance the catalytic activity of hemin; both intramolecular parallel G-quadruplexes and intermolecular four-stranded parallel G-quadruplexes can enhance the catalytic activity of hemin; the addition of T nucleotides to the 5′-end of a G-tract confers corresponding G-quadruplex greatly enhanced catalytic activity, whereas the addition of T nucleotides to the 3′-end of the G-tract has little effect; the high catalytic activity of hemin in the presence of some short-stranded G-rich sequences may be a result of the reduction of the acidity of the bound hemin cofactor. These studies provide more information for the DNA-hemin peroxidase model system, may help to elucidate the structure-function relationship of peroxidase enzymes and to develop novel, highly efficient peroxidase-liking DNAzymes. As a sequence of such an investigation, a new Hg²⁺ detection method was developed.     

Interactions of aluminum(III) with the biologically relevant ligand d-ribose

Aluminum(III) can be absorbed when it is appropriately complexed. There are several plasma components which can bind weakly Al(III). Many proteins bind Al(III) in solution quite strongly. Carbohydrates bearing an abundance of electronegative functional groups can interact with metal cations. In solution, d-ribose exists as a mixture at equilibrium of many isomers and only a few of them bear a ‘complexing’ sequence of the hydroxyl groups. The presence of d-ribose in an Al(III) solution experiences a decrease of its Brönsted-acid sites. The lowering of the Brönsted acidity of an Al(III)-d-ribose mixture suggests the existence of attractive interactions (‘association’) between Al(III) ion and the complexing sequence of the hydroxyls of d-ribose. There is enhancement in the stability of the interaction complexes between Al(III) and d-ribose through strong intramolecular hydrogen bonding, which offers the possibility to investigate the kinetics of the subsequent proton release reactions. On the basis of the kinetic results, it may be concluded that proton release reactions, which are associated with the complexation reactions, are associatively activated. The complexes (Al(H₂O)_6−n(d-ribose_−nH)⁽³⁻ⁿ⁾⁺) resulting from the various ‘complexing’ forms of d-ribose are formed at mainly acidic pH. As the pH increases, the values of the activation enthalpy, ΔH^≠, are changing, because of the formation of mixed hydroxo-complexes (Al(H₂O)_6−n−m(OH)_m(d-ribose_−nH)^(3−n−m)+); finally, OH⁻ displaces d-ribose from the coordination sphere of Al(III) in a rather slow process, i.e. with high values of ΔH^≠; the activation enthalpy values, ΔH^≠, decrease with the progression of the displacement, becoming finally very small due to the formation of a precipitate. Chelate coordination of d-ribose with some divalent and trivalent metal ions has been also reported.     

Thermomorphic fluorous phosphines as organocatalysts for Michael addition reactions

The fluorous phosphines P[(CH₂)_mR_fn]₃ (R_fn = (CF₂)_n−1CF₃; m/n = 2/8, 3/8, 3/10) are efficient nucleophilic catalysts of Michael addition reactions. They can be easily recycled based upon their highly temperature-dependent solubilities (thermomorphism), with recovery by simple liquid/solid phase separation. The phosphonium salt formed by reaction of the nucleophilic phosphine with the α,β-unsaturated system appears to be a significant component of the catalyst rest state.     

Formation and structural refinements of tunneled intergrowth phases in the Ga2O3-In2O3-SnO2-TiO2 system

Over 100 samples were prepared as (Ga,In)₄(Sn,Ti)_n−4O_2n−2, n=6, 7, and 9 by solid-state reaction at 1400 °C and characterized by X-ray diffraction. Nominally phase-pure beta-gallia-rutile intergrowths were observed in samples prepared with n=9 (0.17?x?0.35 and 0?y?0.4) as well as in a few samples prepared with n=6 and 7. Rietveld analysis of neutron time-of-flight powder diffraction data were conducted for three phase-pure samples. The n=6 phase Ga_3.24In_0.76Sn_1.6Ti_0.4O₁₀ is monoclinic, P2/m, with Z=2 and a=11.5934(3) Å, b=3.12529(9) Å, c=10.6549(3) Å, β=99.146(1)°. The n=7 phase Ga_3.24In_0.76Sn_2.4Ti_0.6O₁₂ is monoclinic, C2/m, with Z=2 and a=14.2644(1) Å, b=3.12751(2) Å, c=10.6251(8) Å, β=108.405(1)°. The n=9 phase Ga_3.16In_0.84Sn₄TiO₁₆ is monoclinic, C2/m, with Z=2 a=18.1754(2) Å, b=3.13388(3) Å, c=10.60671(9) Å, β=102.657(1)°. All of the structures are similar in that they possess distorted hexagonal tunnels parallel to the [010] vector.     

A sensitive fluorescence reagent for the determination of aldehydes from alcoholic beverage using high-performance liquid chromatography with fluorescence detection and mass spectrometric identification

A pre-column derivatization method for the sensitive determination of aldehydes using the tagging reagent 2-[2-(7H-dibenzo[a,g] carbazol-7-yl)-ethoxy] ethyl carbonylhydrazine (DBCEEC) followed by high-performance liquid chromatography with fluorescence detection and APCI-MS identification has been developed. The chromophore of fluoren-9-methoxy-carbonylhydrazine (Fmoc-hydrazine) reagent was replaced by 2-[2-(7H-dibenzo[a,g] carbazol-7-yl)-ethoxy] ethyl functional group, which resulted in a sensitive fluorescence tagging reagent DBCEEC. DBCEEC could easily and quickly labeled aldehydes. The maximum excitation (300 nm) and emission (400 nm) wavelengths did not essentially change for all the aldehyde derivatives. Derivatives were sufficiently stable to be efficiently analyzed by high-performance liquid chromatography. The derivatives showed an intense protonated molecular ion corresponding m/z [M + (CH₂)_n]⁺ in positive-ion mode (M: molecular weight of DBCEEC, n: corresponding aldehyde carbon atom numbers). The collision-induced dissociation of protonated molecular ion formed fragment ions at m/z 294.6, m/z 338.6 and m/z 356.5. Studies on derivatization demonstrated excellent derivative yields in the presence of trichloroacetic acid (TCA) catalyst. Maximal yields close to 100% were observed with a 10 to 15-fold molar reagent excess. Separation of the derivatized aldehydes had been optimized on ZORBAX Eclipse XDB-C₈ column with aqueous acetonitrile as mobile phase in conjunction with a binary gradient elution. Excellent linear responses were observed at the concentration range of 0.01-10 nmol mL⁻¹ with coefficients of >0.9991. Detection limits obtained by the analysis of a derivatized standard containing 0.01 nmol mL⁻¹ of each aldehyde, were from 0.2 to 1.78 nmol L⁻¹ (at a signal-to-noise ratio of 3).     

Palladium nitrosyl carboxylate clusters: Synthesis and reactivity. X-ray structures of Pd4(μ-CO)2(μ-NO)(μ-RCO2)5 (R = Pr, Bu)

New palladium nitrosyl carboxylate complexes Pd₈(CO)_4−m(NO)_m(NO₂)₄(RCO₂)₈ (m = 2, 4) were obtained by the treatment of palladium carbonyl carboxylates clusters cyclo-Pd_n(μ-CO)_n(μ-RCO₂)_n (n = 6) (1) with gaseous nitrogen monoxide. These complexes are the products of CO substitution in early described Pd₈(CO)₄(NO₂)₄(RCO₂)₈ clusters. By adding an excess of corresponding acid to reaction mixture Pd₄(CO)₂(NO)(RCO₂)₅ complexes were obtained, their structures were determined by X-ray diffraction analysis. These clusters are intermediate products of transformation of 6-nuclear initial clusters into various 8-nuclear complexes. This fact demonstrates that carboxylate ligands can be used as stabilizers for intermediate unstable polynuclear palladium compounds.     

Electrochemical and bioelectrocatalytical properties of novel block-copolymers containing interacting ferrocenyl units

The electrochemical characterization of three different polystyrene-b-polybutadiene block-copolymers, functionalized with diferrocenylsilane units, is reported. The PB-blocks have been functionalized with different fractions of electronically communicated, PS_m-PB_n−p (HSiMeFc₂)_p units, where m = 615, n = 53, p = 39 (1), m = 375, n = 92, p = 76 (2) and m = 455, n = 204, p = 170 (3). Electrochemical characterization has been carried out both in solution and after electrochemical deposition onto platinum electrodes. The bioelectrocatalytical properties of electrodes modified with the polymers in the nicotinamide dinucleotide (NADH) and glucose oxidase (GOx) oxidations have been investigated as a function of the constitution and structure of the polymers. The analytical properties of electrodes modified with these polymers as sensors of NADH and GOx are described. In addition, an amperometric biosensor for glucose, prepared by electrostatic immobilization of glucose oxidase onto a platinum electrode modified with one of the ferrocenyl block-copolymers as an example, has been developed.     

Volumetric properties of (an organic compound + di-n-butyl ether) atT = 298.15 K

Excess molar volumes V_m^Eof {di- n -butyl ether (DBE)  +  a monofunctional organic compound} have been determined atT =  298.15 K over the whole composition range by means of a vibrating-tube densimeter. TheV_m^E values were either positive (propylamine, or butylamine, or acetone, or tetrahydrofuran  +  DBE) or negative (methanol, or butanol, or diethyl ether, or cyclopentanone, or acetonitrile  +  DBE). Markedly asymmetric V_m^Ecurves were displayed by (DBE  +  methanol) and (DBE  +  acetonitrile). Partial molar volumes __ V_m^oat infinite dilution in DBE, both from this work and the literature, were analysed in terms of an additivity scheme, and the group contributions thus obtained were discussed and compared with analogous results in water. DBE revealed a greater capability of distinguishing between polar and non-polar solutes, as well as in discriminating differently shaped molecules (unbranched, branched, cyclic). The limiting slopes of apparent excess molar volumes are evaluated and briefly discussed in terms of solute–solute and solute–solvent interactions.     

Evolution of the metallicity in the Li n H m clusters as a function of m: evidence for a segregation

The unimolecular decomposition of metal rich Li _n H _m ⁺ clusters (1 ≤ m ≤ 6, n ≤ 22 and (n ? m) > 3) is studied. The evaporative rates of the mixed clusters display features characteristic of metallic clusters. This confirms and extends to a larger size range the previous results obtained by photoionization and absorption cross section measurements. The evaporative rates are simulated by considering that there is a segregation between a metallic Li _n-m ⁺ part and an insulating (LiH)_m part in the mixed cluster.